Many rear air suspensions allow twist in the axle during roll events (opposite wheel travel in the vertical direction) to provide roll stiffness. However, because of the manner in which the axle is attached to such suspensions, unwanted forces are transferred to the axle.
One approach to a solution is shown in U.S. Pat. No. 4,310,171 to Merkle. Merkle shows a vehicle axle attachment having a control arm having two parallel plates shaped to form horizontally spaced lugs at one to attach to the vehicle hangar bracket and vertically spaced lugs at the opposite end to attach to the axle. The vertically spaced lugs are rigidly connected to the axle by way of a flange. With a rigid connection, the roll rate of this arrangement is fixed.
A suspension arrangement in accordance with the invention includes a control arm provided as a beam having a first end with a single arm and a second end with an upper arm and a lower arm diverging to define a Y-shape, the first end being connectable to a vehicle frame, and the second end being connectable to a vehicle axle disposed between the upper and lower arms. A bushing arrangement mounts the arms to the vehicle axle, the bushing arrangement having an upper portion connecting to the upper arm and a lower portion connecting to the lower arm, the bushing having a selected rate.
The suspension according to the invention improves the transfer of twisting forces to the axle by constraining the axle between two arms of the control arm. The axle is twisted about the center of torsion, allowing increased twist to the axle without the introduction of an extra bending moment in the axle. The invention advantageously adds adjustment of the response of the suspension by way of the axle bushings.
According to another aspect of the invention, the control arm is formed of a first beam and a second beam in parallel, spaced relation, the first beam and second beam being interconnected to the axle by the bushing arrangement. The spacing may be varied, according to the invention, to provide the desired mechanical advantage for twisting the axle. The first beam and second beam are relatively thin plate members that provide a weight advantage in the assembly while providing sufficient strength and stiffness in the vertical direction. In addition, forming the first beam and second beam as thin plates provides some lateral flexibility to the suspension assembly for accommodating lateral suspension events.
The invention thus provides an improvement in roll rate by a control arm that is much stiffer in the vertical direction than in the lateral direction.
According to the invention, the first beam and second beam are interconnected only by the axle bushing arrangement and a second bushing arrangement mounting the beams to the vehicle frame.
According to another aspect of the invention, the first beam and second beam are connected to form the control arm with the axle end bushing arrangement disposed between the respective upper arms and lower arms.
Preferably, the bushing arrangement includes two upper bushings and two lower bushings.
According to another aspect of the invention, the rate of the bushings that attach the beam to the axle may be varied to influence certain suspension characteristics. For example, making the two top bushings stiffer in the fore/aft direction and relatively softer in the vertical direction and making the bottom bushings softer in the fore aft direction and relatively stiffer in the vertical direction can improve roll steer, lateral stiffness, roll rate, toe stiffness and camber stiffness.
According to yet another aspect of the invention, the first beam and second beam each include a plate section and flanges extending perpendicularly from edges of the plate section, wherein the first beam and second beam are mutually disposed with the respective flanges extending in opposite directions.
According to another aspect of the invention, the suspension arrangement further includes a hanger mountable to the frame, the first end of the control arm being pivotally mounted to the hanger.
According to yet another aspect of the invention, the suspension arrangement further includes a spring mountable between the axle and the frame. The spring may be disposed between a seat on an arm mountable to and extending from the axle and a bracket mountable to the frame.